August 24, 2009

Upward Lightning Caught On Camera

The rare phenomenon, known as "gigantic jets," was photographed during tropical storm Cristobal last year.

The gigantic jets shot more than 40 miles high, Duke Professor Steven Cummer and colleagues wrote in the journal Nature Geoscience.

"Despite poor viewing conditions as a result of a full moon and a hazy atmosphere, we were able to clearly capture the gigantic jet," said Cummer.

"What we were able to conclusively show is that these are not just sparks that come out of the thunderstorm and travel upward and tickle the upper atmosphere," he told BBC News.

"They actually deliver to the upper atmosphere as much electric charge as the very strong lightning strokes to ground."

Since 2001, only five images of gigantic jets have been captured. They are difficult to capture because they occur within the blink of an eye.

The Duke University team caught a one-second view and magnetic field measurements that are now giving scientists a much clearer understanding of these rare events.

"This confirmation of visible electric discharges extending from the top of a storm to the edge of the ionosphere provides an important new window on processes in Earth's global electrical circuit," said Brad Smull, program director in NSF's Division of Atmospheric Sciences, which funded the research.

"They are essentially upward lightning from thunderclouds that deliver charge just like conventional cloud-to-ground lightning. What struck us was the size of this event," said Cummer.

His team also took radio measurements of the event near Durham, North Carolina.

Whereas a conventional lightning bolt follows a six-inch channel and travels about 4.5 miles down to earth, the gigantic jet recorded by the scientists contained multiple channels and traveled about 40 miles upward, they said.

"Given that reservoirs of electric charge in thunderstorms are the sources for both lightning and gigantic jets, and that both events involve contact between these reservoirs and a very large conducting surface, it is not surprising that their charge transfers are comparable," Cummer said.

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Image Caption: Trees form a horizon from which a gigantic jet emerges; the thunderstorm is 200 miles away. Credit: Steven Cummer